1. Field of the Invention
This invention relates to distributed lighting systems, particularly for room lighting and vehicles, in which optical fibers distribute light from a central source to a number of different optical loads, with the fibers performing various control functions such as switching, oscillation and headlight beam control.
2. Description of the Related Art
Conventional automobile lighting systems use separate light bulbs for each lighting function, resulting in some cases in more than one hundred different light bulbs. This is not a desirable situation for energy efficiency and reliability. Furthermore, some of the bulbs are typically placed in inconvenient locations, making them difficult to access and increasing maintenance costs, especially for instrument panel lightings. The bulbs are powered by an electrical wiring network, leading to the possibility of electrical short circuits that are often difficult to locate. The light bulb systems are also subject to breakage in case of impacts, and add to the weight, bulk and expense of the overall vehicle.
An alternate system in which light is distributed from a central light source to various optical loads within a vehicle by means of "light busses" is described in U.S. Pat. No. 4,930,049 to Davenport et al. The light bus network includes a number of optical control functions, such as a switch, turn signal oscillator and dimmer. All of these devices, however, are subject to improvement. In the optical switch, for example (FIG. 9(b) of the '049 patent), a receiving optical fiber is moved into and out of alignment with a light bus by means of a piezoelectric, electromagnetic, pneumatic bimetal or memory metal mechanism. All of these involve a simple bending of the receiving fiber away from the light bus to turn the switch OFF. This does not account for the fact that light typically spreads out when emitted from the end of an optical fiber, and no mechanism is provided for positively blocking the transmission of light from the light bus to the receiving fiber in the OFF position. Furthermore, the system operates "open loop" in the sense that there is no mechanism to confirm that the fiber has been properly positioned.
In the turn signal oscillator of the '049 patent (FIG. 10(b)), the light bus is moved by an externally controlled mechanical rotating arm into and out of alignment with a receiving "optical carrying member". However, no mechanism is provided to assure that the light bus moves all the way into and then out of alignment with the receiving optical carrying member.
In FIG. 11(b) of the patent, an optical dimming mechanism is disclosed in which a "means" 78 in the optical path alters its transparency between substantially clear and substantially cloudy. However, the manner in which this function is accomplished is not described.
A distributed lighting system in which light from a central light source is carried by a series of optical fibers to an array of headlight lenses is described in U.S. Pat. No. 4,868,718 to Davenport et al. In this patent the ends of the fibers are held stationary in alignment with their respective lenses, while optical wedges or rotating flat members are inserted between the fibers and their respective lenses to shift between high and low beams. In a related system described in U.S. Pat. No. 4,949,227 to Finch et al., a movable mask is placed between the fibers and the headlight lenses to form either a high or a low beam pattern, depending upon the position of the mask. Both of these approaches require the insertion of additional mechanical devices between the fibers and the headlight lenses, thus adding to the cost and complexity of the system.
Another headlight system is described in U.S. Pat. No. 4,811,172 to Davenport et al. in which each headlight has a dedicated light source, with separate optical fibers transmitting light from the source to the various lenses of the headlight. A pair of fibers are provided for each lens and are arranged at an angle to each other, with one fiber on the lens axis and the other off-axis. One of the fibers is illuminated to produce a high beam output, and the other to produce a low beam output. This system requires a redundancy in the optical fibers for each headlight lens, and also requires a separate lamp for each headlight.
A light source for a distributed vehicle lighting system is described in U.S. Pat. No. 4,958,263 to Davenport et al. The source consists of a pressurized lamp with quartz light guides merged into portions of its outer surface to provide illumination for the various optical loads within the vehicle. The portions of the lamp that are not merged with the light guides are coated with a diffusive reflective coating that is said to substantially prevent light from being transmitted through the coating, thereby directing all of the light generated by the lamp into the light guides. However, the patent does not describe any control mechanisms such as optical switches or oscillators. A headlight system is shown, but no mechanism for alternating between high and low beams is presented.
While the centralized lighting systems described in the above patents offer advantages over conventional discrete lighting systems, there is also a significant potential reliability problem. If the central light source fails, all or a large section of the lighting system will be lost. The problem is more severe than in discrete lighting systems, in which the loss of a light bulb affects only its single associated component. The described systems do not provide a failsafe mechanism to prevent a severe disruption of the lighting system when the light source fails.